Surgical Anatomy of Supratentorial Midline Lesions

Arteries of the insula
Parasylvian (M 4) and Terminal (M 5) Segments of the MCA
The M 3 segments course laterally to exit the sylvian fissure
and become M 4 segments on the lateral surface of the
hemisphere. The M 4 and M 5 segments consist of 12 main
arteries, which have been documented and named in earlier
publications according to their territories of supply. 7,9,
34,35 These include lateral orbitofrontal, prefrontal, precentral,
central, anterior parietal, posterior parietal, angular,
temporooccipital, posterior temporal, middle temporal,
anterior temporal, and temporal polar arteries (Fig. 1). No
branches from the M 4 and M 5 segments were observed to
supply the insula.
Arteries Supplying the Insula
The insula receives its blood supply predominantly
from the M2 segment. An examination of 40 hemispheres
revealed 75 to 104 insular arteries originating from this
segment. However, in 22 hemispheres (55%), between
one and six insular arteries arose from the distal M1 segment
and supplied the region of the limen insulae. In 10
hemispheres (25%), one or two insular arteries arose from
the M3 segment and supplied the region of either the superior
or inferior periinsular sulcus. We observed no branches
to the insula from the M4 and M5 segments. In each
hemisphere, an average of 96 insular arteries (range 77–
112 insular arteries) were found supplying the insula
(Figs. 4 upper, 6, and 7). The average diameter of these arteries
was 0.23 mm (range 0.1–0.8 mm). An average of
9.9 insular arteries (range four–14 insular arteries) in each
hemisphere resembled perforator arteries, and their distribution
occasionally reached as far as the corona radiata
(Figs. 7 and 8). We sometimes observed a larger caliber
insular artery that coursed along the surface of the insula
and then looped laterally, providing branches to both
the insula and the medial surface of the operculum. We
named this artery the “insuloopercular artery” (Fig. 4 upper).
Approximately 85 to 90% of insular arteries were
short and supplied the insular cortex and extreme capsule;
10% were medium sized and also supplied the claustrum
and external capsule; and the remaining 3 to 5% were long
and extended as far as the corona radiata (Fig. 8). The long
insular arteries were perforator-like and mostly located in
the posterior region of the insula. The putamen, globus
pallidus, and internal capsule were vascularized by the
LLAs (Fig. 4 lower). The external capsule was found to be
the border of territories supplied by the LLAs and the insular
arteries. We observed no gross communications between
the insular arteries and LLAs.
Discussion
The MCA is the most complex of the cerebral vessels.
This artery supplies almost the entire lateral surface of the
hemisphere, as well as the insula, the lentiform nucleus,
and the internal capsule. Microsurgical anatomy of the
MCA, especially that of the M1 segment and the LLAs,
has been examined and analyzed in detail in many studies.
2–4,6–14,16,18–22,24–36 It is well known that chronic hypertension
induces pathological changes in cerebral vessels,
resulting in either their occlusion or rupture, which leads
to lacunar infarctions or intracerebral hemorrhages, re-
J. Neurosurg. / Volume 92 / April, 2000
FIG. 3. Drawings showing anatomical variations in the cortical
branches of M 1. A: The M 1 segment gave rise to a temporal
branch in 57.5% of the hemispheres. B: The M 1 segment gave
rise to temporal and frontal branch arteries in 35% of the hemispheres.
C: The M 1 segment gave rise to a frontal branch in 2.5%
of the hemispheres. D: The M 1 segment gave rise to no major
cortical branches (only LLAs and uncal arteries) in 5% of the hemispheres.
The LLAs are denoted by dotted lines. A 1 = precommunicating
segment of the ACA.
spectively. The most common site of a spontaneous intracerebral
hemorrhage is the lenticular region, observed in
35 to 50% of patients. 25 Because lenticular structures are
located within the territory of the LLAs and Heubner’s artery,
when hemorrhage is suspected to have occurred from
these vessels, the importance of being familiar with the
anatomy of the LLAs is clearly of great relevance. Marinković
and colleagues 12 observed between three and 18
LLAs (average nine LLAs). They explored and described
every single origin of the LLAs and found no communications
among these vessels in either their extracerebral 12
or intracerebral segments. 13 Duret 3 has claimed that the
LLAs course laterally as far as the putamen. He has asserted,
moreover, that the more lateral structures, such as the
claustrum and external capsule, derive their blood supply
from vessels penetrating the insula. Beevor 2 has concurred
with Duret, 3 confirming this lateral boundary of the LLAs.
Both have stated that no communications exist among the
lateral LLAs and the insular arteries. Shellshear 23 injected
a coloring agent into the MCA after ligating the M 2 segment.
He discovered injection material in the striatum,
claustrum, and external capsule, whereas the insular cortex
was clear. Our study confirmed that the external capsule
is the margin of territories supplied by the LLAs and
the insular arteries. We found no gross evidence of communications
between these two arterial systems. Insular
arteries can be coagulated to devascularize intrinsic tumors
and vascular malformations in the insular region,
without damaging the vascularization of the putamen and
internal capsule. 37–39 However, long insular arteries should
be preserved because of possible infarction in the corona
radiata (Fig. 8). Some striate AVMs have been observed to
receive their blood supply from these two groups of arteries,
which indicates the potential existence of microcommunications
between the LLAs and the insular arteries
(Fig. 9).
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